it depends on what you mean by "experience." I think buzz is easily superior to twitter, but I use twitter because the community I engage with is there.

does the existence of picasa's online albums somehow harm google because only some people use them?

Here’s my discussion on the Buzz user experience, from a year ago. http://alanhogan.com/buzz-is-already-dead

(tl;dr: Too distracting, not very skimmable, awkward social aspects including too many non-friends showing up.)